Shock absorber with frequency dependent passive valve

1. A shock absorber comprising:

a pressure tube defining a fluid chamber for containing a working fluid;

a reserve tube, with the pressure tube being disposed within the reserve tube to define a working fluid reservoir between the pressure tube and the reserve tube;

a piston assembly disposed within the pressure tube and secured to a piston rod, the piston assembly disposed dividing said fluid chamber into an upper working chamber and a lower working chamber;

a base valve assembly disposed between the lower working chamber and the working fluid reservoir, the base valve assembly including a frequency dependent valve system operable to:

act as a bypass to allow a portion of the working fluid to pass therethrough during high frequency movements of the shock absorber during each compression stroke of the piston assembly, to thus provide a minimum degree of damping; and

to at least substantially interrupt a flow of the working fluid therethrough during low frequency movements of the shock absorber during each of the compression strokes, to thus provide increased damping;

the frequency dependent valve system further including:

a valve seat plate in contact with a distal end of a spool valve;

an interface member in contact with the valve seat plate;

a biasing element for biasing the interface member into contact with the valve seat plate and the distal end of the spool valve;

a valve body disposed between the spool valve and the valve seat plate, the valve body having a bypass flow path in communication with the working fluid reservoir; and

wherein a pressure of the working fluid acting on the spool valve during a compression stroke, and during a high frequency movement of the shock absorber, operates to force the interface member away from the valve seat plate permitting a flow of the working fluid therebetween.

2. The shock absorber of claim 1 , wherein the interface member includes a land which contacts the valve seat plate.

3. The shock absorber of claim 2 , wherein the base valve assembly further comprises an upper valve pin having a bore therethrough in communication with an axial bore of the spool valve.

4. The shock absorber of claim 1 , wherein the frequency dependent valve system includes:

a first chamber formed adjacent a first side of the spool valve;

a second chamber formed between the spool valve and the valve body;

wherein during the high frequency movements of the shock absorber the time is insufficient to displace the working fluid from the second chamber, and does not allow the spool valve to move a sufficient distance to generate a force on the interface member which is sufficiently high to prevent the interface member from being lifted off of the valve seat plate, and thus the working fluid is able to lift the interface member from the valve seat plate to allow a flow of the working fluid therebetween; and

wherein during the low frequency movements of the shock absorber the movement of the spool valve is increased which displaces the fluid from the second chamber, and which forces the spool valve towards the lower housing member against the biasing force being provided by the biasing element, and thus generates a sufficient force that prevents the working fluid from lifting the interface member off of the valve seat plate.

5. The shock absorber of claim 1 , wherein the base valve assembly further comprises:

an upper valve pin having a bore extending axially therethrough;

a cylinder end member for receiving the upper valve pin;

a valve connection member coupled to the cylinder end member and including a plurality of holes through which the working fluid flows, and a cavity within which the spool valve is disposed, the bore of the upper valve pin being in communication with the bore of the spool valve;

a lower valve pin in contact with the biasing element; and

a lower housing member secured to the valve connection member which supports the lower valve pin in a stationary manner.

6. The shock absorber of claim 5 , further comprising a sealing element disposed between a peripheral wall portion of the spool valve and the cavity of the valve connection member.

7. A shock absorber comprising:

a pressure tube defining a fluid chamber for containing a working fluid;

a reserve tube, with the pressure tube being disposed within the reserve tube to define a working fluid reservoir between the pressure tube and the reserve tube;

a piston assembly disposed within the pressure tube and secured to a piston rod, the piston assembly dividing said fluid chamber into an upper working chamber and a lower working chamber;

a base valve assembly disposed between the lower working chamber and the working fluid reservoir, the base valve assembly including a frequency dependent valve system including:

an axially slidable spool valve responsive to a flow of the working fluid during a compression stroke;

a valve seat plate in contact with a distal end of the spool valve;

an interface member in contact with the valve seat plate;

a biasing element for biasing the interface member into contact with the valve seat plate;

the spool valve operable to experience only a relatively small degree of movement during a high frequency, short duration compression stroke of the piston assembly, thus allowing fluid pressure flowing through the spool valve to urge the interface member away from the valve seat plate and allow a flow of the working fluid therebetween to the working fluid reservoir, to thus reduce a damping provided by the shock absorber; and

the spool valve operable during a low frequency, long duration compression stroke to experience a movement of a greater axial distance than during the high frequency compression stroke, which causes the spool valve to apply sufficient pressure to the valve seat plate to at least substantially close off a flow of the working fluid between the interface member and the valve seat plate, to thus increase a damping provided by the shock absorber.

8. The shock absorber of claim 7 , wherein the frequency dependent valve assembly further comprises:

a first chamber adjacent a first side of the spool valve upon which fluid pressure from the working fluid acts during the compression stroke of the piston assembly;

a second chamber at least partially defined between a valve body and a second side of the spool valve; and

wherein during the low frequency compression stroke the spool valve moves a sufficient distance to displace the working fluid in the second chamber, and applies sufficient pressure to the valve seat plate to at least substantially interrupt a flow of the working fluid through the spool valve.

9. The shock absorber of claim 7 , wherein the interface member includes a land formed thereon for contacting the valve seat plate.

10. The shock absorber of claim 7 , wherein the base valve assembly includes an upper valve pin in flow communication with a bore of the spool valve.

11. The shock absorber of claim 10 , further comprising a cylinder end member in which the upper valve pin is disposed.

12. The shock absorber of claim 7 , wherein the base valve assembly includes a lower valve pin in contact with the biasing element.

13. The shock absorber of claim 12 , further comprising a lower housing member coupled to the valve connection member, and operable to hold the lower valve pin stationary within the base valve assembly.

14. The shock absorber of claim 7 , further comprising a valve connection member having a cavity within which the spool valve is disposed for sliding axial movement.

15. The shock absorber of claim 14 , further comprising an annular end stop member disposed within the cavity adjacent the first side of the spool valve, defining a stop for axial travel of the spool valve.

16. The shock absorber of claim 15 , wherein the lower valve pin includes a boss portion about which the biasing element is mounted.

17. The shock absorber of claim 14 , wherein the valve connection member includes a plurality of radially arranged holes for allowing fluid flow therethrough during both low frequency and high frequency compression strokes of the piston assembly.